Soldering flux formula for improving soldering reliability of product and preparation process

Abstract

The invention relates to the technical field of scaling powder production, in particular to a scaling powder formula for improving the soldering-aid reliability of a product and a preparation process. The scaling powder formula comprises diethylene glycol monohexyl ether; an organic active acid; ethylene glycol phenyl ether; a thixotropic agent, a copper corrosion inhibitor and a surfactant; according to the flux, high-activity organic acid is compounded with glutaric acid and adipic acid, a gradient volatile solvent system diethylene glycol monohexyl ether and ethylene glycol phenyl ether and precise thixotropic control is adopted, so that the voidage of a welding spot is smaller than or equal to 7.3% and is superior to that of a commercial rosin-based flux in the prior art, the average value is 40-50%, the wetting angle is smaller than or equal to 26 degrees, and the flux is adaptive to a surface difficult to weld; the performance is stable after 1000-hour high-temperature and high-humidity aging, no electromigration risk exists, no cleaning is achieved, and the high-reliability scene requirements of automotive electronics (AEC-Q200), 5G communication, circuit boards / chips and the like are met; 5% of the thixotropic agent provides enough collapse resistance, does not influence fluidity, realizes thixotropic balance, has high residue insulativity and no moisture absorption risk, and prevents residues from interfering with automatic optical detection.

Description

Technical Field

[0001] This invention relates to the field of flux production technology, specifically a flux formulation and preparation process for increasing the reliability of product soldering. Background Technology

[0002] Flux is a chemical substance used in the soldering process, typically composed of ingredients such as rosin, organic acids, or resins. Its main functions are to clean the soldering surface, promote soldering quality, prevent oxidation, and improve the reliability and quality of the solder joint. The fundamental purpose of flux is to remove obstacles, ensuring that the molten solder can form a strong metallurgical bond with the base metal. It does not participate in the formation of the solder joint itself, but it is absolutely necessary for the successful wetting and spreading of the solder. Flux technology has evolved from simple natural rosin into a highly refined field of specialized chemistry. While it doesn't constitute the final solder joint, it is crucial in determining the success and quality of soldering. Its development has consistently revolved around the balance between "activity" and "corrosiveness," as well as meeting the growing demands for environmentally friendly manufacturing. Modern no-clean flux technology embodies this art of balance, requiring halogen-free flux. Existing fluxes, containing halogens, are harmful to the environment and human health. The electronics industry's strong push for halogen-free fluxes places extremely high demands on the activator system. It needs to achieve sufficient activity under halogen-free conditions, while also possessing compatibility and detectability. The flux must be compatible with various PCB surface treatments, component plating, and subsequent conformal coating materials. Simultaneously, its residues must not interfere with automated optical inspection. Therefore, the inventors have proposed a flux formulation and preparation process to increase the reliability of product soldering, solving the aforementioned technical problems of achieving no-clean operation and preventing interference with optical inspection after coating. Summary of the Invention

[0003] To overcome the shortcomings mentioned above, the invention aims to provide a technical solution that can solve the above problems.

[0004] A flux formulation for increasing the reliability of product soldering, comprising the following components by weight: Diethylene glycol monohexyl ether 50.0 parts to 60.0 parts; organic active acid 20.0 parts to 30.0 parts; ethylene glycol phenyl ether 1.0 parts to 10.0 parts; thixotropic agent 1.0 parts to 10.0 parts; copper corrosion inhibitor 0.1 parts to 0.5 parts; surfactant 0.2 parts to 0.8 parts; the remainder is trace stabilizer or deionized water, with a total amount not exceeding 2.0 parts; The flux is free of rosin, halogens, and strong alkaline substances, and has a viscosity of 80-200 Pa·s at 25°C. The residue after welding can be completely volatilized or form a non-hygroscopic film. This formula uses a high proportion of organic active acids. Glutaric acid has the characteristics of high activity and easy volatility, which can effectively remove Cu / Sn oxide film in the preheating stage. Adipic acid regulates the reaction rate and avoids boiling and gas production. The combination of the two achieves the effect of strong deoxygenation and complete volatilization, reducing gas residue from the source. The measured void ratio is ≤7.3%. Fluorocarbon / polyether siloxanes reduce the surface tension of molten solder from ~500 mN / m to <300 mN / m; With a wetting angle as low as 26°, it can still spread well on difficult-to-solder surfaces such as OSP, ENIG, and Immersion Silver, avoiding defects such as cold solder joints and poor wetting. This formula does not contain rosin, halogens, or strong alkalis, has no resin carbonization residue, and no corrosive ions. The residue is a completely volatile organic compound or an inert film that does not absorb moisture. After high temperature and high humidity aging, the insulation resistance is ≥3×10¹²Ω. There is no electrochemical migration or copper dendrites, and the long-term reliability far exceeds that of traditional rosin-based fluxes. Thixotropic agents impart shear-thinning properties to the flux, resulting in good flowability during printing and resistance to collapse after standing. It supports ultra-fine pitch printing such as 0.3 mm CSPs and 0201 components, with edge collapse <15μm. The viscosity at 25℃ is 80–200 Pa·s, matching the requirements of stencil / dispensing processes. Diethylene glycol monohexyl ether has a high boiling point, providing a stable carrier, while ethylene glycol phenyl ether has a medium boiling point, forming a gradient evaporation. Together, they prevent sudden vaporization of the solvent during reflux, preventing bubbles from being drawn into the solder joints, and are suitable for air or nitrogen reflux; compatible with mainstream lead-free alloys such as SAC305 and SAC405.

[0005] Furthermore, the organic active acid includes 15.0 to 25.0 parts of glutaric acid and 5.0 to 10.0 parts of adipic acid; the total content of organic active acid is ≥20%, ensuring that the metal oxide film is fully removed during the preheating stage at 150–220℃ and completely decomposed and volatilized before the peak temperature of 240℃.

[0006] Furthermore, the thixotropic agent is one of fumed silica, hydrogenated castor oil, or polyamide wax; when the thixotropic agent is surface-hydrophobically treated and has a particle size of 7–20 nm, and is added at an amount of 3.0%–7.0%, it can enable the flux to have shear-thinning properties, and the anti-slump height after printing is ≥0.15 mm.

[0007] Furthermore, the copper corrosion inhibitor is benzotriazole (BTA) or methylbenzotriazole (TTA).

[0008] Furthermore, the surfactant is a fluorocarbon surfactant or a polyether-modified siloxane.

[0009] Furthermore, the ratio of diethylene glycol monohexyl ether to ethylene glycol phenyl ether is 5:1 to 10:1, which synergistically regulates the solvent evaporation gradient and avoids bumping and gas generation during the reflux stage.

[0010] A flux preparation process for increasing the soldering reliability of products, the process comprising the following steps: S1: Main solvent mixing; Diethylene glycol monohexyl ether and ethylene glycol phenyl ether were added to a dual planetary mixer and stirred at 400 rpm for 10 minutes at 40–50 °C to form a homogeneous solvent system. S2: Dissolved in organic acids; Heat to 60–70°C, add glutaric acid and adipic acid in batches, control the feeding rate to prevent clumping, and stir at 500 rpm for 40–60 minutes until completely dissolved to form a transparent solution; S3: Introduction of functional additives; Cool to 45–50°C, add benzotriazole and surfactant sequentially, and stir for 20 minutes; then slowly sprinkle in the thixotropic agent, increase the speed to 600 rpm, and disperse at high speed for 30 minutes to ensure uniform formation of the thixotropic network; S4: Vacuum degassing and homogenization; Transfer the material to a vacuum mixer and stir at 300 rpm for 15 minutes under a vacuum of ≤ -0.095 MPa to thoroughly remove microbubbles and volatile impurities. S5: Cooling and filtration; After naturally cooling to 25±2℃, the flux is filtered through a 0.45 μm polytetrafluoroethylene (PTFE) filter membrane to obtain a finished flux product that is free of particles, gel, and bubbles. S6: Packaging and storage; It is sealed in a brown glass bottle or aluminum foil composite bag filled with nitrogen and stored in a cool, dark place at 5±2℃. The shelf life is ≥12 months.

[0011] Furthermore, in step S3, the thixotropic agent is applied as a dry powder using a combination of high-speed shearing to avoid introducing additional moisture from the pre-dispersed solvent.

[0012] Furthermore, after the flux is printed on the stencil and left to stand for 30 minutes, the edge collapse width is ≤20μm, which meets the printing requirements of 0.3mm CSP packaging.

[0013] Furthermore, the flux is applied to solder paste or liquid flux, and after nitrogen reflow soldering, the void ratio of the solder joint X-ray area is ≤8%, and the surface insulation resistance of the residue is ≥1×10¹²Ω.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This flux achieves a solder joint void rate of ≤7.3%, which is superior to the average value of 40-50% of existing commercial rosin-based fluxes, through the combination of highly active organic acids, glutaric acid and adipic acid, a gradient volatile solvent system of diethylene glycol monohexyl ether + ethylene glycol phenyl ether, and precise thixotropic control. It also achieves a wetting angle of ≤26°, making it suitable for difficult-to-solder surfaces. After 1000 hours of high temperature and high humidity aging, it maintains stable performance with no risk of electromigration, achieving cleaning-free operation and meeting the high reliability requirements of automotive electronics (AEC-Q200), 5G communication, circuit boards / chips, and other scenarios. 5% thixotropic agent provides sufficient anti-collapse properties without affecting flowability, achieving a thixotropic balance. Its effect is superior to existing products. This formulation ratio can achieve a void rate reduction of >50%, a wetting angle improvement of >12°, higher residual insulation, and no risk of moisture absorption, thus avoiding interference of its residues with automatic optical detection. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to specific embodiments.

[0016] In this embodiment, please refer to a specific implementation of a flux formulation for increasing the reliability of product soldering. Calculated by mass percentage, it consists of the following components: Diethylene glycol monohexyl ether 50.0 parts to 60.0 parts; organic active acid 20.0 parts to 30.0 parts; ethylene glycol phenyl ether 1.0 parts to 10.0 parts; thixotropic agent 1.0 parts to 10.0 parts; copper corrosion inhibitor 0.1 parts to 0.5 parts; surfactant 0.2 parts to 0.8 parts; the remainder is trace stabilizer or deionized water, with a total amount not exceeding 2.0 parts; The flux is free of rosin, halogens, and strong alkaline substances, and has a viscosity of 80-200 Pa·s at 25°C. The residue after welding can be completely volatilized or form a non-hygroscopic film. This formula uses a high proportion of organic active acids. Glutaric acid has the characteristics of high activity and easy volatility, which can effectively remove Cu / Sn oxide film in the preheating stage. Adipic acid regulates the reaction rate and avoids boiling and gas production. The combination of the two achieves the effect of strong deoxygenation and complete volatilization, reducing gas residue from the source. The measured void ratio is ≤7.3%. Fluorocarbon / polyether siloxanes reduce the surface tension of molten solder from ~500 mN / m to <300 mN / m; With a wetting angle as low as 26°, it can still spread well on difficult-to-solder surfaces such as OSP, ENIG, and Immersion Silver, avoiding defects such as cold solder joints and poor wetting. This formula does not contain rosin, halogens, or strong alkalis, has no resin carbonization residue, and no corrosive ions. The residue is a completely volatile organic compound or an inert film that does not absorb moisture. After high temperature and high humidity aging, the insulation resistance is ≥3×10¹²Ω. There is no electrochemical migration or copper dendrites, and the long-term reliability far exceeds that of traditional rosin-based fluxes. Thixotropic agents impart shear-thinning properties to the flux, resulting in good flowability during printing and resistance to collapse after standing. It supports ultra-fine pitch printing such as 0.3 mm CSPs and 0201 components, with edge collapse <15μm. The viscosity at 25℃ is 80–200 Pa·s, matching the requirements of stencil / dispensing processes. Diethylene glycol monohexyl ether has a high boiling point, providing a stable carrier, while ethylene glycol phenyl ether has a medium boiling point, forming a gradient evaporation. Together, they prevent sudden vaporization of the solvent during reflux, preventing bubbles from being drawn into the solder joints, and are suitable for air or nitrogen reflux; compatible with mainstream lead-free alloys such as SAC305 and SAC405.

[0017] The organic active acid comprises 15.0 to 25.0 parts of glutaric acid and 5.0 to 10.0 parts of adipic acid; the total content of organic active acid is ≥20%, ensuring that the metal oxide film is fully removed during the preheating stage at 150–220℃ and completely decomposed and volatilized before the peak temperature of 240℃; the thixotropic agent is one of fumed silica, hydrogenated castor oil, or polyamide wax; the thixotropic agent is surface-hydrophobic treated, with a particle size of 7–20 nm, and when added at an amount of 3.0% to 7.0%, it can give the flux shear-thinning properties, resulting in a slump resistance height ≥0.15 mm after printing; the copper corrosion inhibitor is benzotriazole (BTA) or methylbenzotriazole (TTA); the surfactant is a fluorocarbon surfactant or a polyether-modified siloxane; the ratio of diethylene glycol monohexyl ether to ethylene glycol phenyl ether is 5:1 to 10:1, which synergistically regulates the solvent evaporation gradient and avoids bumping and gas generation during the reflux stage.

[0018] A flux preparation process for increasing the soldering reliability of products, the process comprising the following steps: S1: Main solvent mixing; Diethylene glycol monohexyl ether and ethylene glycol phenyl ether were added to a dual planetary mixer and stirred at 400 rpm for 10 minutes at 40–50 °C to form a homogeneous solvent system. S2: Dissolved in organic acids; Heat to 60–70℃, add glutaric acid and adipic acid in batches, controlling the addition rate to prevent agglomeration. Stir at 500 rpm for 40–60 minutes until completely dissolved to form a transparent solution. During this stage, maintain a temperature of 65℃, combine batch acid addition with 55 minutes of stirring. Glutaric acid and adipic acid have melting points >95℃ and are highly water-soluble, but easily agglomerate in the organic phase. This process ensures complete molecular-level dissolution, forming a transparent homogeneous system. This avoids uneven activity caused by undissolved particles, which can affect local wetting failure and prevents boiling over during reflow, gas encapsulation, and increased voids. By employing temperature control and batch processing, the flux activity consistency is improved by >95%, with batch-to-batch variation <3%. S3: Introduction of functional additives; Cool to 47°C, add benzotriazole and surfactant in sequence, and stir for 20 minutes; then slowly sprinkle in thixotropic agent, increase the speed to 600 rpm, and disperse at high speed for 30 minutes to ensure uniform formation of thixotropic network. In step S3, the thixotropic agent is added as dry powder in combination with high-speed shearing to avoid introducing additional moisture from the pre-dispersed solvent. This stage employs "dry powder application and 600 rpm high-speed shearing" to avoid the introduction of moisture or impurities by traditional pre-dispersion liquids. Thixotropic agents such as fumed silica fully deagglomerate under high-speed shearing, forming a three-dimensional hydrogen bond network to achieve shear thinning. The edge collapse is ≤20 μm 30 minutes after printing, which can be adapted to advanced packages such as 0201 components and 0.3 mm CSP / BGA, and eliminates bridging and misalignment. S4: Vacuum degassing and homogenization; The material is transferred to a vacuum mixing vessel and stirred at 300 rpm for 15 minutes under a vacuum of ≤ -0.095 MPa to thoroughly remove microbubbles and volatile impurities. This stage removes air entrained by stirring and trace amounts of gas dissolved in the solvent. The gas content of the flux body is ≤0.5 vol% to prevent bubbles from being released from the inside of the flux and encapsulated by the molten solder during reflow. This step, combined with reflow profile optimization, is a key process step to achieve a void ratio of ≤8%.

[0019] S5: Cooling and filtration; After naturally cooling to 25±2℃, the flux is filtered through a 0.45 μm polytetrafluoroethylene (PTFE) membrane to obtain a particle-free, gel-free, and bubble-free finished flux. This step of filtering through a 0.45 μm PTFE membrane removes undispersed thixotropic agent agglomerates, dust, and gel impurities, ensuring that the flux is particle-free, fiber-free, and gel-free. This prevents the Type 5 / 6 solder paste stencil from clogging and avoids foreign matter in the solder joints that could lead to electromigration or a decrease in mechanical strength. S6: Packaging and storage; Nitrogen-filled and sealed in brown glass bottles or aluminum foil composite bags, stored in the dark at 5±2℃, shelf life ≥12 months; This step involves refrigerating the product in a nitrogen-filled, light-protected environment at 5°C. This inhibits the oxidation of organic acids and the degradation of surfactants, prevents thixotropic agents from settling or flocculating, and extends the product's shelf life to ≥12 months, which is longer than the conventional 6-month shelf life of fluxes. After opening, the product's performance remains stable, reducing yield fluctuations on the production line caused by material aging.

[0020] Compared with traditional flux preparation processes, the process of this invention features segmented temperature control and long-term dissolution, resulting in more uniform activity. This improves upon the rapid mixing of traditional processes and eliminates the uneven activity caused by incomplete acid dissolution. High-vacuum degassing is used to suppress voids at the source, avoiding the situation where the flux contains gas due to the lack of vacuum degassing. Furthermore, 0.45μm PTFE filtration reduces the residual particles left by ordinary filtration of ≥5 μm.

[0021] After the flux is printed on the stencil and left to stand for 30 minutes, the edge collapse width is ≤20μm, which meets the printing requirements of 0.3 mm CSP packaging. When the flux is applied to solder paste or liquid flux, the X-ray area ratio of the solder joint void rate is ≤8% after nitrogen reflow soldering, and the surface insulation resistance of the residue is ≥1×10¹²Ω.

[0022] Table 1 shows the experimental results for different group proportions. Table 1 shows that all implementation groups are free of rosin, halogens, and strong alkalis; the total solvent content is >90%; the remainder is trace stabilizer.

[0023] Table 1 Table 2 shows the performance test data. Table 2 Based on the table above, it can be seen that: Group B had the lowest void ratio of 7.3% in the example, with a moderate proportion of organic acid of 26%, which can fully deoxidize while avoiding excessive acid decomposition and gas generation in the later stage of reflux. The wetting angle was 26°, and the synergistic effect of surfactant and BTA was the best, achieving rapid spreading. The 5% thixotropic agent provides sufficient anti-collapse properties without affecting flowability, achieving a thixotropic balance. Compared with existing commercial rosin-based fluxes, it outperforms existing products. This formulation ratio can achieve a void rate reduction of >50%, a wetting angle improvement of >12°, higher residual insulation, and no risk of moisture absorption, thus avoiding interference from its residues with automatic optical detection.

[0024] Table 3 shows the reflow soldering curve parameters. Table 3 Table 4 shows the accelerated aging test data (85℃ / 85% RH, 1000 hours). Table 4 Table 5 is a comparison table with traditional rosin-based fluxes. Table 5 The data above shows that the void ratio increase in all components of the present invention is less than 12%, indicating that the residue is stable and there is no hygroscopic expansion or secondary gas generation. In contrast, commercial rosin-based fluxes, due to resin residue hygroscopicity, experience a void ratio increase of over 43%, a two-order-of-magnitude decrease in insulation resistance, and exhibit typical electrochemical migration. Based on the comparative data of the above commercial rosin-based fluxes, it can be seen that Group B in the examples has the best overall performance, with low initial voids, high aging stability and excellent insulation, and its performance is higher than that of commercial rosin-based fluxes.

[0025] This invention's flux achieves a solder joint void rate of ≤7.3%, superior to the average value of 40-50% for commercially available rosin-based fluxes, through a highly active organic acid compound of glutaric acid and adipic acid, a gradient volatile solvent system of diethylene glycol monohexyl ether + ethylene glycol phenyl ether, and precise thixotropic control. It also achieves a wetting angle of ≤26°, making it suitable for difficult-to-solder surfaces. After 1000 hours of high-temperature and high-humidity aging, its performance remains stable with no risk of electromigration, eliminating the need for cleaning and meeting the high reliability requirements of automotive electronics (AEC-Q200), 5G communication, circuit boards / chips, and other applications.

[0026] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A flux formulation for increasing the reliability of product soldering, characterized by, calculated by mass parts ratio, It consists of the following components: Diethylene glycol monohexyl ether 50.0 parts to 60.0 parts; organic active acid 20.0 parts to 30.0 parts; ethylene glycol phenyl ether 1.0 parts to 10.0 parts; thixotropic agent 1.0 parts to 10.0 parts; copper corrosion inhibitor 0.1 parts to 0.5 parts; surfactant 0.2 parts to 0.8 parts; the remainder is trace stabilizer or deionized water, with a total amount not exceeding 2.0 parts; The flux is free of rosin, halogens, and strong alkaline substances, has a viscosity of 80–200 Pa·s at 25°C, and the residue after welding can be completely volatilized or form a non-hygroscopic film.

2. The flux formulation for increasing the reliability of product soldering according to claim 1, characterized in that, The organic active acid comprises 15.0 to 25.0 parts of glutaric acid and 5.0 to 10.0 parts of adipic acid; The total content of organic active acids is ≥20%, ensuring that the metal oxide film is fully removed during the preheating stage of 150–220℃ and completely decomposed and volatilized before the peak temperature of 240℃.

3. The flux formulation for increasing the reliability of product soldering according to claim 1, characterized in that, The thixotropic agent is one of fumed silica, hydrogenated castor oil, or polyamide wax; Thixotropic agents, after surface hydrophobic treatment, with a particle size of 7–20 nm, can impart shear-thinning properties to flux when added at a concentration of 3.0%–7.0%, resulting in a slump resistance height ≥0.15 mm after printing.

4. The flux formulation for increasing the reliability of product soldering according to claim 1, characterized in that, The copper corrosion inhibitor is benzotriazole (BTA) or methylbenzotriazole (TTA).

5. A flux formulation for increasing the reliability of product soldering according to claim 1, characterized in that, The surfactant is a fluorocarbon surfactant or a polyether-modified siloxane.

6. A flux formulation for increasing the reliability of product soldering according to claim 1, characterized in that, The ratio of diethylene glycol monohexyl ether to ethylene glycol phenyl ether is 5:1 to 10:1, which synergistically regulates the solvent evaporation gradient and avoids bumping and gas generation during the reflux stage.

7. A flux preparation process for increasing the reliability of product soldering, characterized in that: This preparation process is used in the flux formulation for increasing the soldering reliability of a product as described in any one of claims 1-6, and the preparation process includes the following steps: S1: Main solvent mixing; Diethylene glycol monohexyl ether and ethylene glycol phenyl ether were added to a dual planetary mixer and stirred at 400 rpm for 10 minutes at 40–50°C to form a homogeneous solvent system. S2: Dissolved in organic acids; Heat to 60–70°C, add glutaric acid and adipic acid in batches, control the feeding rate to prevent clumping, and stir at 500 rpm for 40–60 minutes until completely dissolved to form a transparent solution; S3: Introduction of functional additives; Cool to 45–50°C, add benzotriazole and surfactant sequentially, and stir for 20 minutes; then slowly sprinkle in the thixotropic agent, increase the speed to 600 rpm, and disperse at high speed for 30 minutes to ensure uniform formation of the thixotropic network; S4: Vacuum degassing and homogenization; Transfer the material to a vacuum mixer and stir at 300 rpm for 15 minutes under a vacuum of ≤ -0.095 MPa to thoroughly remove microbubbles and volatile impurities. S5: Cooling and filtration; After naturally cooling to 25±2℃, the flux is filtered through a 0.45μm polytetrafluoroethylene (PTFE) filter membrane to obtain a finished flux product that is free of particles, gel, and bubbles. S6: Packaging and storage; It is sealed in a brown glass bottle or aluminum foil composite bag filled with nitrogen and stored in a cool, dark place at 5±2℃. The shelf life is ≥12 months.

8. A flux formulation for increasing the reliability of product soldering according to claim 7, characterized in that, In step S3, the thixotropic agent is applied as a dry powder using a high-speed shearing method to avoid introducing additional moisture from the pre-dispersed solvent.

9. A flux formulation for increasing the reliability of product soldering according to claim 7, characterized in that, After the flux is printed on the stencil and left to stand for 30 minutes, the edge collapse width is ≤20μm, which meets the printing requirements of 0.3 mm CSP packaging.

10. A flux preparation process for increasing the reliability of product soldering according to claim 7, characterized in that: The flux is applied to solder paste or liquid flux, and after nitrogen reflow soldering, the void ratio of the solder joint X-ray area is ≤8%, and the surface insulation resistance of the residue is ≥1×10¹²Ω.

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